Marine fouling refers to the settlement and growth of organisms on submerged, manufactured surfaces and has been has been a problem since the dawn of maritime history. Colonization of submerged surfaces by marine organisms occurs within days to weeks of the surface entering the marine environment and, given the ever-increasing presence of maritime structures (underwater cables, generators, pipelines etc), the battle against fouling organisms is becoming an increasingly significant challenge. The need for effective methods to control marine fouling is of paramount importance to the international shipping industry.
Antifouling coatings prevent the settlement of marine organisms, generally by killing larval foulers through the action of broad spectrum biocides such as organotin or copper compounds. Although extremely effective, environmental degradation resulting from the use of organotin compounds was so severe that marine paint companies voluntarily withdrew these paints from the market in 2003, and the IMO banned their use in 2008 (International Convention on the Control of Harmful Anti-fouling Systems on Ships, entered into force 17 Sep. 2008). Although copper and biocide booster containing paints are still widely available, their use is not desirable since they have the potential to accumulate in the marine environment (Voulvoulis, 2006).
Current commercial marine coatings can be divided into two classes: antifouling and foul-release. Antifouling coatings use broad-spectrum biocides which kill foulers by oxidation or, more usually, exposure to toxic metal ions. Foul-release coatings are mainly silicon based polymers that are easy to clean, however the best of these usually also contain additives and catalysts that kill organisms. As noted above, legislation and agreements, based on the recognition of the environmentally unacceptable consequences of toxic antifouling agents such as tributyl tin in coatings, have prompted interest to develop new less environmentally pernicious coatings.
An approach reported by Teo et al (an inventor of the present application) in U.S. Ser. No. 11/265,833, is the use of pharmaceuticals as antifouling agents. It has been demonstrated that pharmaceuticals may disrupt the metamorphosis of fouling organisms. Commercially available pharmaceuticals, with their known synthesis, chemical properties and primary mechanism of action in vertebrates and in humans, were screened as potential sources of antifouling agents. Whilst eight pharmaceuticals with promising bioactivity were reported, there remains the problem that these pharmaceuticals may accumulate in the marine environment. Furthermore, some of these pharmaceuticals suffer from delivery problems because of poor solubility in sea water.
A further alternative to broad spectrum biocides is small, biodegradable organic molecules that inhibit the settlement of marine organisms. Such molecules should not be recalcitrant in the environment and should be “benign by design”. To this end, Teo et al recently demonstrated the antifouling potential of a family of simple α,α-disubstituted amides (selected examples shown below) on larval barnacles and bacterial biofilms (PCT/SG2009/000175). These molecules are predicted to breakdown rapidly in the marine environment.

Numerous organic biocides have been used as additives into tin-free paints, however, the direct incorporation of small molecules into coating systems presents a number of issues. First, the release of the organic antifoulants must be sustained for several years in order to minimize the requirement for repainting of the vessel prior to scheduled dry-docking. In addition, many currently employed organic antifoulants are toxic to marine foulers, which, with increased use could have an unfavorable impact on the marine ecosystem in the event of accumulation. The physical properties of the organic antifoulants can also have a profound impact on the integrity of a commercially available coating system, which in the absence of metal-based binders may require reformulation of coating systems.
Crucially, the mechanism by which the small molecule is incorporated into the coating system should permit retention of the activity of the small molecule. It is to be expected that structural modifications of the small molecule to impact on activity so that incorporating any active molecule into a coating system would be challenging.